The present invention relates to a positive resist composition, particularly to a chemically amplified positive resist composition, which is high in transparency to the vacuum ultraviolet laser, particularly to the F2 excimer laser beam, and is high in sensitivity. The present invention further relates to a process for forming a resist pattern using the composition.
In recent years, resist compositions have been used in the production of semiconductor devices and liquid crystal devices. Particularly, a chemically amplified resist composition is a resist for utilizing the catalytic action of an acid formed by the irradiation of an activating energy ray. Such resist has high sensitivity and high resolution and makes it possible to reduce the amount of an compound (i.e., photoacid generator) for generating an acid by the irradiation of an activating energy ray. Such resist has two types, positive and negative types, and contains two basic components, a photoacid generator and a film-forming component that is subject to a change in solubility in an basic aqueous solution by the action of the acid generated.
Hitherto, a polyhydroxystyrene resin, of which a part of the hydroxyl groups is optionally protected by substituting solubility reducing groups capable of being dissociated in the presence of an acid, has widely been used as the film-forming component (resin component) of resist compositions, due to its high transparency to the KrF excimer laser beam (wavelength: 248 nm).
As a trend toward finer semiconductor devices, the process of using the KrF excimer laser beam (248 nm) is now under a replacement with the process of using the ArF excimer laser beam (193 nm). It is, however, almost impossible to use benzene-ring-containing resins (e.g., the above-mentioned polyhydroxystyrene) in the patterning process using the ArF excimer laser beam, since those resins are insufficient in transparency.
The following two publications disclose examples of the above-mentioned resins. Japanese Patent Laid-open Publication JP-A-4-39665 discloses an acrylic ester resin having a skeletal structure of adamantane in the ester moiety of the molecule. JP-A-8-82925 discloses an acrylic or methacrylic ester resin having a terpenoid skeleton such as menthol.
As a trend toward further finer semiconductor devices, there has been a demand for a process using vacuum ultraviolet laser, particularly F2 excimer laser, which is shorter than ArF excimer laser in wavelength. It is, however, almost impossible to use the above-mentioned resins, for example, polyhydroxystyrene, or a non-fluorine-containing acrylic resins in the patterning process using a vacuum ultraviolet laser such as the F2 excimer laser (157 nm), since those resins are insufficient in transparency. Thus, there is an urgent demand for a novel resist composition that is transparent in a shorter wavelength range of not greater than 157 nm. In connection with this, perfluoro compounds are generally known to have high transparency in this shorter wavelength. These compounds are, however, insoluble in organic solvents generally used in the resist patterning technique. Thus, it is practically impossible to use these compounds for the patterning process using the F2 excimer laser.
It is therefore an object of the present invention to provide a positive resist composition that is high in transparency to vacuum ultraviolet laser beams, particularly the F2 excimer laser beam, and high in sensitivity and in solubility in organic solvents used in the resist patterning technique.
It is another object of the present invention to provide a process for forming a resist pattern using such composition.
It is still another object of the present invention to provide a process for producing such composition.
According to the present invention, there is provided a positive resist composition for a laser having a wavelength in a vacuum ultraviolet region, said composition comprising (a) an acrylic resin which is subject to a change in solubility in a basic aqueous solution, the acrylic resin comprising an acrylic or methacrylic acid ester unit comprising an ester moiety comprising a fluorine-containing group; and (b) a photoacid generator.
According to the present invention, there is provided a process for forming a resist pattern. This process comprises (1) providing the positive resist composition; (2) applying the composition to a substrate, thereby forming a resist film on the substrate; (3) exposing a portion of the resist film to a radiation of a laser in a vacuum ultraviolet region (1-190 nm); and (4) developing the resist film with the basic aqueous solution by removing the exposed portion of the resist film, thereby forming the resist pattern.
According to the present invention, there is provided a process for producing the positive resist composition. This process comprises (1) polymerizing an acrylic or methacrylic acid ester comprising an ester moiety comprising a fluorine-containing group, thereby obtaining the acrylic resin; and (2) adding the photoacid generator to the acrylic resin.